I had an unusual experience last eve in doing an update to Big Sur, which I've had installed since it came out, with no issues. I clicked the update, and it said downloading Big Sur, at a 3.86 GB download! Hmmm? Then, at 400 MB down it stopped downloading. Wouldn't budge. So I closed the window, clicked update again, and the download started over. After about an hour I completed the installation, again, of macOS Big Sur on my 2019 MBA.

This morning, Big Sur opened up and works just fine again, as it did before the update. Just an 'interesting' experience, if that's the correct word.

Jim Hamm